The importance in the world marketplace for the bulk chemical calcium magnesium acetate ("CMA") has been dramatically increasing.
One important use for CMA is as an organic, biodegradable, non-corrosive deicing salt, suitable to replace rock salt (sodium chloride) as the predominate road deicing salt. Each year, millions of tons of sodium chloride and calcium chloride are used for deicing highways. Agoos, A., Chemical Week, 144.5, 18-19, (1989); and Marynowski, C. W., J. L. Jones, D. Tuse, and R. L. Broughton, I&EC Product Res. Devel., 24, 457-465, (1985). Sodium chloride is used almost universally because of its excellent deicing properties, wide spread availability, and low delivered costs. Because of its higher costs, calcium chloride is only used when required for effective deicing at lower temperatures.
However, despite its advantages, the costs to society caused by the use of rock salt are enormous. For example, the cost of corrosion to bridges and automobiles, and the contamination of ground water, have been estimated to be nearly fifty times the delivered cost of sodium chloride. Hudson, L. R., Presentation at IGT Conference "Energy from Biomass Waste XI," Mar. 18, 1987. Unfortunately, the cost of currently available alternate, nonpolluting and noncorrosive, deicing materials and methods are too high to attract widespread commercial use.
To address the corrosion problems with rock salt, several corrosion inhibitors are commercially available, such as Cargill's CG-90.RTM. and Great Salt Lake Mineral and Chemicals' Freezgard.RTM. and Qwiksalt.RTM.. These products, which use phosphate or lignin based corrosion inhibitors, are as effective as salt for deicing, and reduce corrosion. Unfortunately, they do nothing to eliminate the pollution problem posed by the use of salt. The phosphate based inhibitors may, in fact, increase pollution by the addition of phosphate to the highway runoff.
One of the most promising alternate deicing materials is CMA, a mixture of calcium and magnesium acetate, with a Ca/Mg ratio typically between about 1 and 0.5. Dunn, S. A., and R. U. Schenk, Federal Highway Administration Report FHWA/RD-79/108, Washington, D.C, 1980. Acetate compounds are attractive replacements because they are nontoxic, noncorrosive to metals, and substantially as effective as rock salt. Calcium and magnesium ions provide improved performance of the mixture over use of the individual ions, and are readily available in high magnesium dolomitic lime and limestone. CMA has been successfully tested in extensive studies in the northern United States and Canada.
A second important use for CMA is as an additive to coal-fired combustion units, such as those used by the electric utilities. In such a use, the CMA acts as a catalyst to facilitate combustion, resulting in more coal being burned for a given size unit. Also, the CMA acts to remove the sulfur in the coal by reacting with the sulfur to form solid calcium sulfate, which is recoverable from the stack gases. Thus, the use of CMA in this manner reduces the serious problem of acid rain. Wise, D. L., Y. A. Levendis, and M. Metahalic (eds.), Calcium Magnesium Acetate, Amsterdam: Elsevier Science Publishers, (1991).
These and other important uses for CMA have made it a potentially major industrial chemical. Unfortunately, current commercial methods of producing CMA make it too expensive to be commercially feasible for most applications. Currently, CMA is commercially available, believed to be produced from glacial acetic acid derived from petroleum. The estimated cost of commercially available CMA is approximately twenty times that of rock salt (sodium chloride). Present commercial manufacturing techniques for CMA include combining acetic acid, derived, for example, from petroleum, with calcium and magnesium, for example, from high magnesium dolomitic limestone. However, the cost of separately producing, distilling, and purifying acetic acid, and subsequently reacting it with a calcium and magnesium ion source to form CMA, results in the present high price of commercially-available CMA.
In addition to petroleum sources, acetic acid has been produced through several biological routes. Ghose, T. K. and A. Bhadra, M. Moo-Yung (ed.), Comprehensive Biotechnology, 3, 710-729 (1985). Anaerobic bacteria have been studied extensively because of the high theoretical yield. Anaerobic bacteria used to convert inexpensive carbohydrates from starch or cellulosic materials (e.g., glucose or xylose) to acetic acid, include strains of Clostridium thermoaceticum, C. thermocellum, C. thermoautotrophicum, Acetogenium kivui or Acetobacter aceti. See, e.g., Toda, K., Y. S. Park, T. Asakura, C. Y. Cheng and H. Ohtake, Appl. Microbiol. Biotechnol., 30, 559-563, (1989); Ljungdahl, L. G., L. H. Carreira, R. J. Garrison, N. E. Rabek, L. F. Gunter and J. Wiegle, U.S. Department of Transportation, Fed. Highway Adm. Rept. FHWA/RD-86/117, Washington, D.C., (1986); and Lynd, L. R., H. E. Grethlein, and R. H. Wolkin, Appl. Environ. Microbiol., 55, 3131-3139, (1989). However, recovery of dilute acetic acid by distillation of the fermentation broths is extremely energy demanding, and therefore expensive.
Some anaerobic organisms produce acetic acid by the homofermentative pathways which produce three moles of acetic acid from one mole of glucose with no loss of carbon by carbon dioxide. In contrast, acetic acid producing aerobic organisms, such as certain strains of Bacillus, produce only two moles of acetic acid from one mole of glucose. The two-thirds yield for aerobic organisms in producing acetic acid has, prior to this invention, made the commercial production of acetic acid by aerobic organisms to be considered economically impractical, especially when coupled with the extremely expensive recovery by distillation. Ghose, T. K. and A. Bhadra, M. Moo-Yung (ed.), Comprehensive Biotechnology, 3, 710-729 (1985).
While the use of aerobic bacteria to produce acetic acid has previously been considered not to be economically feasible, aerobic bacteria of the genus Bacillus are currently used industrially. Bacillus are used in the production of industrial enzymes, such as amylases used to modify starch in the brewing, printing, fabric, or food industries; the production of proteases, used in laundry detergents; and in the production of glucose isomerase, used in the commercial isomerization of glucose to high fructose corn syrups. Many of these industrial processes have used mesophilic Bacillus. High temperature Bacillus species have also been used for the production and identification of thermostable proteins.
Accordingly, there is a need for a direct method of producing CMA at a cost that would make it feasible to use it in a wide range of commercial applications, such as, to replace rock salt as the primary highway deicer. There is also a need for a unique high temperature Bacillus species capable of the sustained production of substantial quantities of acetic acid at low pH and at high salt concentrations.
Accordingly, the present invention provides a method for the direct biological production of calcium magnesium acetate using a novel combination of an aerobic thermophilic bacterium of the genus Bacillus, capable of sustained production of substantial quantities of acetic acid at low pH, and high salt concentrations. The rapid, sustained production of acetic acid, is carried out in the method of the present invention in the presence of a neutralizing source of calcium and magnesium ions, such as dolomitic lime at a pH sufficiently low to dissolve the dolomitic lime, or other neutralizing source of calcium and magnesium ions.